The victim: The Arctic sea ice, which melted to a record low area
last year.

"The
Great Arctic Cyclone of August 2012" arose in Siberia on Aug.
2 and crossed the Arctic Ocean to Canada, lasting an unusually
long 13 days. The cyclone hit a pressure minimum of 966 millibars
on Aug. 6, the lowest ever recorded for an Arctic storm. The
stronger the pressure gradient, or difference in pressure, the
stronger the winds associated with a storm.

Since the storm, which was equal in
strength to a hurricane, tore across the Arctic, scientists
have wondered whether its winds and waves were a guilty party in
the disappearing Arctic sea ice.

Guilty or not guilty?

To solve the mystery, climate scientists from the University of
Washington performed the equivalent of a forensic exam: They ran
a computer simulation of last summer's weather and compared it
against a second scenario that was identical, except that there
was no cyclone.

"The storm was enormous," study co-author Axel Schweiger, a polar
scientist in the university's Applied Physics Laboratory, said in
a statement. "The impact on the ice was immediately obvious, but
the question was whether the ice that went away during the storm
would have melted anyway because it was thin to begin with."

Though the storm had a huge impact on sea ice while it passed,
within two weeks, the effect diminished, lead author Jinlun
Zhang, also a scientist in the university's Applied Physics
Laboratory, said in the statement.

"Thus without the storm, 2012 would still have produced a record
minimum," the authors report in their study, which appears online
this week in the journal Geophysical Research Letters.

Warmed from below

The research also revealed an unusual mechanism for the
cyclone-related melting. A study published Dec. 15, 2012, in the
same journal
focused on winds breaking up the ice or driving ice floes
into areas of warmer water.

But the University of Washington team found that during the
storm, the ice melted largely from warm ocean water churned up by
the passing storm. Melting quadrupled during the storm, and the
rate of ice loss doubled, the study found.

In the Arctic summer, ocean water becomes stratified from melting
ice, according to a statement from the university. A layer of
ice-cold fresh watersits just beneath the sea ice. But about 65
feet (20 meters) below the surface, there is a layer of denser,
saltier water that has been gradually warmed by the sun's rays.

When the cyclone swept over the drifting ice floes, underside
ridges churned up the water, bringing sun-warmed seawater to the
ice's bottom edge and causing it to melt, the study suggests.